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1 Which features of UK farmland are important in retaining territories 2 of the rapidly declining Turtle Dove Streptopelia turtur? 3 JENNY C DUNN1* 4 ANTONY J MORRIS1 5 1 6 Bedfordshire, SG19 2DL. UK. Centre for Conservation Science, RSPB, The Lodge, Potton Road, Sandy, 7 8 9 10 * Author and address for correspondence: 11 12 13 Short title: Turtle Dove breeding habitat selection 14 15 Keywords: nesting habitat, foraging habitat, competition, habitat selection, migratory 16 bird 17 18 19 20 21 Capsule: Turtle Doves continue to show a strong population decline; territories were 22 more likely to be retained in areas with more nesting habitat, and more suitable 23 foraging habitat. 24 Aim: To determine which features of farmland in England are important for retaining 25 Turtle Dove territories 26 Methods: Fifty-eight grid squares with recent records of territorial Turtle Doves were 27 re-surveyed, and squares retaining Turtle Dove territories compared with those from 28 which Turtle Doves had been lost. 29 Results: Turtle Dove territories were detected in 48% of squares resurveyed. When 30 correcting for the 70% detection rate of the survey methodology, territories were 31 present in 66% of squares surveyed suggesting a 34% decline over a two-year period. 32 Established scrub and hedgerows >4 m tall positively influenced Turtle Dove 33 presence and abundance, as did standing water. Bare ground and fallow had positive 34 effects on turtle dove abundance whereas grazed land negatively impacted abundance. 35 Conclusion: The positive effects of area of established scrub and volume of large 36 hedgerow are likely to represent a declining density of birds selecting the best quality 37 nest sites. We suggest instead that foraging habitat may be limiting distribution. 38 39 40 41 42 43 Introduction 44 45 Numbers of both farmland and migratory birds have been declining since the 1970s 46 (Eaton, et al. 2010), and understanding the cause of these declines is crucial in 47 determining strategies to aid population recovery. The European Turtle Dove 48 Streptopelia turtur is the UK’s only migratory dove, over-wintering in sub-Saharan 49 Africa and relying on a source of seed food on European farmland during the summer 50 months in order to raise its young (Murton, et al. 1964; Browne & Aebischer 2003). 51 The UK population declined by 91% between 1970 and 2009, and the decline is 52 ongoing (Eaton, et al. 2011), a trend that is paralleled by a 69% decline across Europe 53 since 1980, leading to this species being one of the most strongly declining birds in 54 Europe (PECBMS 2010). 55 56 Population declines can usually be attributed to a combination of reductions in habitat 57 or food availability, which have implications for survival and breeding productivity. 58 In the case of the Turtle Dove, an analysis of CBC data between 1965 and 1995 59 concluded that nesting habitat availability on farmland was restricting Turtle Dove 60 distribution, as changes in density were positively related to the amount of hedgerow, 61 scrub and woodland edge on farmland plots (Browne, et al. 2004). Territories also 62 contained a higher proportion of woodland, grassland and other non-cropped habitats 63 that would be expected from availability, and a lower proportion of cropped habitats 64 (Browne & Aebischer 2004), suggesting that the availability of suitable foraging 65 habitat was also important, although to a lesser extent. Productivity per nesting 66 attempt was unchanged between 1941 and 2000, suggesting that nest predation was 67 not important (Browne, et al. 2005), although birds ceased breeding earlier and 68 showed markedly reduced August re-nesting when compared to the 1960s, resulting 69 in half the overall number of fledged young (Browne & Aebischer 2004). 70 71 Over-winter survival of Turtle Doves is strongly related to cereal production in 72 Africa, suggesting that conditions on wintering grounds are also important for this 73 species (Eraud, et al. 2009) and it has been suggested that a combination of breeding 74 and over-wintering factors are responsible for population trends (Thaxter, et al. 2010); 75 however, the reduction in the number of fledged young is by itself sufficient to 76 explain the population decline (Browne & Aebischer 2004). Thus, understanding the 77 drivers of the decline in reproductive output is essential if we are to understand and 78 reverse the mechanisms responsible for the negative population trend. 79 80 This study aimed to identify sites retaining territorial Turtle Doves and to compare 81 these to sites from which Turtle Dove territories have been lost within the past two 82 years. Whilst individual Turtle Doves tend not to be site faithful (Browne & 83 Aebischer 2001), the same sites are used by birds year after year (BBS data). We did 84 not aim to determine changes in occupancy as a response to changing habitat; indeed, 85 we ensured that habitat change at our survey sites was minimal through examination 86 of maps and talking to landowners. Instead, we aimed to detect more subtle 87 differences between preferred (still occupied) sites and less preferred sites where 88 territorial Turtle Doves can no longer be detected. This comparison allows us to test 89 four hypotheses: 90 1) An overall decline in numbers means birds arriving in the south east of England 91 (BTO/RSPB/BWI/SOC 2011) are not travelling as far to find suitable breeding 92 territories and thus fewer birds are reaching the northern and western edge of their UK 93 range. 94 2) Territory loss is associated with a reduced availability of nesting habitat. As the 95 population is declining, then birds may just be at lower overall densities and thus 96 selecting areas with better quality nesting habitat. 97 3) Territory loss is associated with a reduction in quality or quantity of suitable 98 foraging habitat. Again, as the population is declining, then birds may be selecting 99 areas with better quality foraging habitat. 100 4) Territory loss is associated with higher abundance of resident columbid species, 101 suggesting either direct competition within suitable habitat for nesting or foraging 102 sites, or indirect competition through increased disease or increased nest predation 103 risk in areas of high nest density. 104 105 Methods 106 Site selection 107 Records of Turtle Dove presence in East Anglia (Bedfordshire, Buckinghamshire, 108 Cambridgeshire, Essex, Hertfordshire, Norfolk and Suffolk) during 2008 and 2009 109 were obtained from sources detailed in the legend to Figure 1. Any records that were 110 recorded at a coarser scale than 1km2 (i.e. tetrads) were excluded unless that record 111 could be isolated to a 1km grid square resolution or higher. 112 113 All observations of transitory (flying) or foraging birds were removed. Records from 114 earlier than 1st June and later than 31st July were also excluded unless breeding 115 activity (calling and/or displaying males, nests or feeding young) was specified, as 116 during these periods it is likely that Turtle Doves will be moving to or from breeding 117 sites (Browne & Aebischer 2004). From these 460 records of breeding Turtle Doves 118 in East Anglia, those with <50% agricultural land (as determined from 1:25,000 119 Ordnance Survey maps) were excluded to leave 379 records from which survey sites 120 could be selected (Fig 1a). 121 122 The remaining squares were prioritised and survey sites were selected according to 123 Turtle Dove density within each grid square, proximity to other records (i.e. focussing 124 on high density areas at the greater than 1km scale) and then according to logistics 125 such as access to landowner details and location to reduce travel distances. 126 127 58 squares (Fig 1b) were surveyed on two occasions by one of three surveyors: the 128 first survey took place between 11th May and 19th June 2010, and the second between 129 21st June and 3rd August 2010; there were at least 4 weeks between the first and 130 second survey at each site (range 28 – 74 days; mean ± SE 46.3 ± 1.7 days). No 131 surveyor bias was evident, with Turtle Doves detected in between 44 and 58% of 132 squares covered by each surveyor. 133 134 Additional single bird and habitat surveys were carried out at three sites where Turtle 135 Doves had been reported breeding during 2010 in order to supplement the sample size 136 of squares with Turtle Doves present for habitat data; breeding activity was confirmed 137 at all three sites. 138 139 Survey methodology 140 Surveys aimed to detect the presence and abundance of singing male Turtle Doves 141 within each survey area. Each survey began at sunrise and lasted between 1 and 2 142 hours (mean ± SE: 91.7 ± 6.8 minutes): 70% of singing Turtle Doves should be 143 detected within the first two hours after sunrise, after which vocal activity decreases 144 markedly, reducing detection rates (Calladine, et al. 1999). The time taken for the 145 survey depended on the structure of habitat (density of field boundaries). Surveys 146 were loosely based on Breeding Bird Survey (BBS) methodology (Marchant, et al. 147 1990): routes followed field boundaries and were designed so that the surveyor 148 crossed each 1km square at least twice (with transects a maximum of 500m apart 149 depending in habitat, and approximately parallel) in order to maximise the surveyor’s 150 chance of hearing singing Turtle Doves should they be present. Where grid squares 151 were consecutive and habitat allowed adequate coverage during the two-hour survey, 152 up to two grid squares were covered on the same morning. Surveyors also assessed 153 the abundance of Woodpigeons Columba palumbus (WP) within each survey area on 154 a categorical scale of 1 – 5 (where 1: 0 – 10 WP; 2: 10 – 25 WP; 3: 25 – 50 WP; 4: 50 155 – 100 WP; and 5: 100+ WP per 1 sq km) to determine whether competition for nest 156 sites or food may influence Turtle Dove distribution. We aimed to include only 157 breeding Woodpigeons in this number, including calling birds, and birds flushed off 158 nests and out of hedgerows, and excluding flocks foraging in fields. Ideally, we 159 would have investigated associations with the abundance of Collared Doves 160 Streptopelia decaocto, as their numbers have increased through natural range 161 expansion as Turtle Dove numbers have declined in England and elsewhere in Europe 162 (Rocha & Hidalgo De Trucios 2000); however Collared Dove numbers at our sites 163 were very low and thus, as the most abundant columbid, Woodpigeon numbers were 164 used as a surrogate for overall columbid abundance as they also show overlap in terms 165 of both nesting and foraging ecology with the Turtle Dove, although they are more 166 generalist (Murton, et al. 1964). 167 168 Habitat data collection 169 Following the first Turtle Dove survey at each site, habitat data were collected from 170 the area surveyed (the entire grid square). Data collected were the crop type in each 171 field, along with details of any non-cropped habitat such as game cover, pollen and 172 nectar or wildflower margins, tracks and paths, field corners, bare ground, trees 173 >10m, scrub, wood, hedgerows, and standing water. The height and width (± 1m) of 174 each length of hedgerow was noted to allow subsequent calculation of hedge volume 175 (height x width x length) in two height categories (<4m and >4 m; Browne & 176 Aebischer 2004). Areas of each crop type or non-cropped habitat were calculated 177 subsequently from 1:10,000 GB Ordnance Survey maps using MapInfo software. 178 179 Statistical analysis 180 Two models were run to determine factors influencing a) the presence and absence of 181 territorial Turtle Doves, and b) the abundance of territorial Turtle Doves. Firstly, we 182 modelled the likelihood of detecting one or more territorial Turtle Doves on a survey: 183 the presence and absence of territorial Turtle Doves within each grid square (over 184 both surveys) was used as the response variable in a general linear model with 185 binomial error structure. In the second model, the maximum abundance of territorial 186 males during either survey was used as the response variable in a generalised linear 187 model with poisson error structure. 188 189 Variables tested against a minimal model were terms related to geographical location, 190 nesting habitat, potential foraging habitat, and Woodpigeon abundance to examine the 191 potential for competition (direct or indirect) for nest or foraging sites. A full list can 192 be found in Appendix 1. All terms pertaining to an area or a volume were log 193 transformed prior to inclusion in any model. 194 195 Variables were screened using the ‘dredge’ function in the ‘MuMIn’ (Burtoń 2012) 196 package in R (R Development Core Team 2012). We fitted models to all possible 197 combinations of explanatory variables (detailed in Appendix 1), then ranked models 198 using second-order Akaike’s Information Criteria (AICc) (Burnham & Anderson 199 2002). AICc measures the relative goodness of fit of a model whilst taking into 200 account the number of variables within each model, and penalising models for the 201 addition of variables. Thus, AICc selects a model with the maximum goodness of fit 202 whilst retaining the minimum number of explanatory variables (Burnham & Anderson 203 2002). 204 205 No single model fit the data better than others, so we averaged the top models using a 206 cut-off of ΔAIC < 2 to provide parameter estimates adjusted for shrinkage according 207 to the number of top models within which each term was found (Burnham & 208 Anderson 2002). 209 210 Results 211 Fifty-eight grid squares with records of territorial Turtle Doves were resurveyed 212 during 2010. Of these, 36 records were from 2008 and 22 from 2009. Turtle Doves 213 were recorded in 28 squares (48 %) during 2010 (Fig 2); of these, 15 (42 %) were 214 from 2008 records and 13 (59 %) from 2009 records. Controlling for the 70 % 215 detection rate of the survey methodology (Calladine, et al. 1999) and correcting for 216 the number of squares within which birds were detected during both surveys, 66 % of 217 squares re-surveyed retained Turtle Dove territories, suggesting a loss of territories 218 from 34 % of squares. 219 220 Habitat influences on Turtle Dove presence or absence 221 Three terms were retained within all eleven top models, and all three had confidence 222 intervals for parameter estimates that didn’t span zero, indicating a high confidence in 223 the effects of these terms. Turtle Doves were more likely to be retained in sites with 224 larger areas of established scrub and greater volumes of hedges, and less likely to be 225 retained in sites with larger areas of grazed land (Tables 1 & 2; Figures 3a & b). The 226 area of fallow and area of standing water were both retained in the top-ranked model, 227 and in six and four of the eleven top models respectively (Table 1), and parameters 228 estimates suggest a small positive influence of these variables on the presence of 229 Turtle Doves, although confidence intervals overlapped zero slightly for both terms 230 (Table 2). Woodpigeon abundance, and the area of young scrub were retained in five 231 and four of the top models respectively (Table 1), and both showed negative 232 associations with Turtle Dove presence; however, confidence in the importance of 233 these terms is lower given that confidence intervals for both terms spanned zero 234 (Table 2). 235 236 Habitat influences on the abundance of territorial Turtle Doves 237 Three terms were retained in all twelve top models investigating associations with 238 Turtle Dove abundance: the area of established scrub, the volume of large hedges, and 239 the area of standing water (Table 3). All three variables had positive impacts on 240 Turtle Dove abundance and none of their confidence intervals spanned zero, 241 indicating a high degree of confidence in the importance of these terms (Table 4). 242 Several other terms were found within the top set of models (Table 3); however, these 243 terms each appeared in between one and three models and parameter estimates 244 indicated low effect sizes (ranging from -0.065 for year of previous record, to 0.015 245 for longitude) with low confidence in these effect sizes as all confidence intervals 246 spanned zero (Table 4). In addition, as we screened a relatively large number of 247 explanatory variables, there is also a possibility of Type 1 error. Thus, whilst the 248 importance of these terms cannot be ignored, there is only weak support for their 249 influence on Turtle Dove abundance. 250 251 252 Discussion 253 Grid squares with recent records of territorial Turtle Doves were resurveyed, and 254 available habitat in squares retaining doves was compared to those from which 255 territories had been lost. Our results indicate a 34% decline in occupancy over a 256 maximum of two years, suggesting a continuing sharp decline in the UK breeding 257 Turtle Dove population. Our sites were selected from previous records based on the 258 abundance of territorial males, so should perhaps have had a higher likelihood of 259 retaining territories than squares with records of only one territory; however, our sites 260 also encompassed areas on the edge of the geographical range detected by our record 261 search, which may have been more likely to lose territories as the Turtle Dove 262 population declines and its range contracts (Fuller, et al. 1995), although we only 263 found weak support for this within our data. Whilst our results may not necessarily be 264 representative of the scale of the population decline, due both to the scale of our 265 study, and as we only examined losses over a two-year period, evidently site 266 occupancy by this species is still decreasing rapidly, supported by BBS data 267 indicating a 21% population decline between 2009 and 2010 (Eaton, et al. 2011). At 268 the current rate of decline, Turtle Doves may be lost as a UK breeding bird by 2021 269 and thus it is crucial that further work attempts to identify the mechanisms 270 underpinning this trend. 271 272 The habitat composition of grid squares retaining Turtle Dove territories was 273 compared to those from which territories have recently been lost and these data were 274 used to test four hypotheses. We found strong support for two of these hypotheses, 275 but only weak support for the other two. First, longitude was retained in only one of 276 the top models investigating Turtle Dove abundance, and none of the top models 277 investigating presence. It is likely our data are not sufficient to detect any effect 278 however, as a range contraction has been occurring in this species for a number of 279 years (e.g. Browne, et al. 2005). No evidence was found to support any effect of 280 latitude, although Turtle Doves are still found further north than our study sites and 281 thus any southwards range shift is unlikely to have been detected. 282 283 Second, Turtle Dove territories were both more likely to be retained, and more 284 abundant, in squares with a greater area of established scrub, and a greater volume of 285 hedgerow >4m high. This concurs with results of previous work that suggested Turtle 286 Doves were limited by the availability of suitable nesting habitat (Browne, et al. 287 2004). Browne, et al. (2004) found Turtle Doves to be associated with hedgerows 288 and woodland edge in farmland, and found territory densities to be much higher in 289 woodland plots than on farmland plots. However, Browne, et al. incorporated 290 woodland and scrub into one category, whereas our results suggest that it is likely to 291 be the scrub component of this that is most important to Turtle Doves as we found a 292 very small negative effect of the area of woodland on the abundance of territories. 293 One interpretation of these results is that Turtle Doves are limited by the availability 294 of suitable nesting habitat. However, this seems unlikely as rates of scrub removal, or 295 deterioration in quality, are unlikely to match the rate of Turtle Dove decline in recent 296 years and territories are being lost from habitat where there is no evidence of 297 destruction or deterioration in quality of scrub in recent years, as determined through 298 examination of maps and talking to landowners. An alternative interpretation, 299 supported by the continuing decline and range contraction shown by the species, is 300 that a lower density of birds results in the fewer birds selecting areas containing the 301 best quality nesting habitat as territories. 302 303 Third, Woodpigeon abundance had a negative impact on the presence of Turtle Dove 304 territories, and a much smaller negative impact on territory abundance. These effect 305 sizes are not large, especially when taking into account the categorical scale of 306 measurement and thus it seems unlikely that this is a result of direct competition for 307 nest sites or food resources, although this cannot be entirely discounted as 308 Woodpigeons begin nesting before the arrival of migrant Turtle Doves. Although 309 Woodpigeons are more cosmopolitan in their nesting habitats, many do nest in areas 310 of large hedgerows and scrub, and it is possible that density-dependent effects such as 311 increased nest predation or disease risk (Chalfoun & Martin 2009, Hochachka & 312 Dhondt 2000) may deter Turtle Doves from nesting in areas containing high nesting 313 densities of the resident species. Historically, the diet of Turtle Doves and 314 Woodpigeons had minimal overlap in early summer as Woodpigeons took mostly 315 unripe cereal grain and Turtle Doves weed seeds (Murton, et al. 1964). However, 316 more recently Browne, et al. (2003) found that 61% of the Turtle Dove diet is now 317 cereal seeds and thus it remains possible that these two species do now compete for 318 food resources. An alternative, and possibly more likely, explanation is that 319 Woodpigeon abundance correlates with an unmeasured habitat variable avoided by 320 Turtle Doves. Whilst the following suggestions are purely speculative, it is possible 321 that microhabitats at either nesting or foraging sites may mean that the negative 322 relationship between Turtle Dove presence and Woodpigeon abundance is habitat- 323 driven. For example, the greater weight and size of Woodpigeons may mean that they 324 nest in slightly more open and structurally supportive scrub than Turtle Doves, whose 325 smaller size allows them to exploit denser scrub with less substantial supporting 326 foliage. Additionally, Woodpigeon often forage at sites with enclosed canopies such 327 as mature oil seed rape crops, whereas Turtle Doves favour open foraging sites 328 (Browne & Aebischer 2003) and thus may be less able to exploit landscapes with a 329 high area of enclosed canopy, e.g. autumn-sown crops. This association requires 330 further investigation before any firm conclusions can be drawn. 331 332 Finally, we found some indications that foraging habitat might be limiting Turtle 333 Dove distribution: the area of grazed land had a negative association with territory 334 presence, and an increased area of fallow had a positive association, albeit small, with 335 territory presence. Additionally, the areas of bare ground and fallow had a weak 336 positive association with territory abundance, which also had a negative association 337 with the area of spring cereals. Bare ground and fallow areas can both potentially 338 provide suitable foraging habitat for Turtle Doves, although there will be considerable 339 variation within these habitats in terms of the suitability of plant species, production 340 of seeds and the accessibility of seeds to foraging birds. The negative effect of grazed 341 land on territory presence suggests that this land type may now be too intensive to 342 provide the weed seeds historically found in Turtle Dove diet (Murton, et al. 1964): 343 vegetation may be too intensively grazed to set seed, herbicide and fertiliser use may 344 reduce the weed species present, and many grazed fields are initially established as 345 monocultures and now lack the diversity historically important in Turtle Dove diet 346 (Murton, et al. 1964). Additionally, Turtle Doves will fly up to 10km to find food 347 (Browne & Aebischer 2003) and thus it is likely that if foraging habitat is limiting the 348 species, we would not detect large effects at the 1km square scale. Of note is the 349 importance of standing water in both our models. As well as farmland, Turtle Doves 350 also nest in reedbed and marsh habitats (Robinson, 2005); whilst this association may 351 be driven by an association between scrub and standing water, the r2 for this 352 correlation within our dataset was only 0.32, suggesting an independent, positive, 353 influence of standing water per se on Turtle Dove presence and abundance. On the 354 breeding grounds, Turtle Doves are known to regularly visit standing water with 355 sparse surrounding vegetation to drink (Naumann, 1833). 356 357 Whilst birds are likely to prioritise territory locations according to suitable nest sites, 358 this does not necessarily mean that food availability is not problematic. That Turtle 359 Doves have halved the number of young they produce since the 1960s (Browne & 360 Aebischer 2004), along with their dietary switch from weed seeds to cereal grain 361 (Browne & Aebischer 2003), suggests that the species may be energetically 362 challenged following migration and during breeding, possibly due to a reduction in 363 diet quality and reduction in food availability early in the breeding season. This 364 reduction in reproductive output is enough, by itself, to explain their population 365 decline (Browne & Aebischer 2004. Currently, agri-environment schemes such as the 366 Entry- and Higher-Level Stewardship Schemes in England offer limited provision for 367 seed-eating birds during the breeding season, as the majority of passerines and 368 columbiformes will consume invertebrates during this time whilst Turtle Dove diet is 369 almost entirely granivorous (Browne & Aebisher 2003). Thus, we suggest that the 370 provision of seed-rich foraging habitat in close proximity to patches of established 371 scrub currently retaining Turtle Dove territories is likely to be beneficial for this 372 species, a hypothesis that will be further tested by a more detailed study of foraging 373 habitat supplementation and use. 374 375 Acknowledgements 376 We would like to thank the many farmers and landowners who allowed access to their 377 land for surveys, and to the BTO and many county recorders and birdwatchers who 378 provided their records of Turtle Doves. Thanks are due to Jenny Bright and Chris De 379 Ruyck for carrying out much of the survey work alongside JCD. This work was 380 funded through the Action for Birds in England (AfBiE) partnership by Natural 381 England and the RSPB. 382 Bibliography 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 Burtoń, K. 2012. MuMIn: Multi-model inference. R package version 1.7.7. http://CRAN.R-project.org/package=MuMIn Browne, S.J. & Aebischer, N.J. 2001. The Role of Agricultural Intensification in the Decline of the Turtle Dove Streptopelia turtur. English Nature Research Report No. 421. English Nature, Peterborough. Browne, S.J. & Aebischer, N.J. 2003. Habitat use, foraging ecology and diet of Turtle Doves Streptopelia turtur in Britain. Ibis 145: 572-582. Browne, S.J. & Aebischer, N.J. 2004. Temporal changes in the breeding ecology of European Turtle Doves Streptopelia turtur in Britain, and implications for conservation. Ibis 146: 125-137. 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Summary of the top models from a binomial GLMM examining which 448 habitat features influence the retention of Turtle Dove territories. 450 451 452 453 454 Y 2 Y Y Y 3 Y Y Y 4 Y Y Y 5 Y Y Y 6 Y Y Y Y 7 Y Y Y Y 8 Y Y Y 9 Y Y Y 10 Y Y Y 11 Y Y Y Weight Area of standing water Y Delta Area of fallow Y AICc Volume of large hedgerows Y df Area of grazed land Y Woodpigeon abundance Area of established scrub 1 Area of young scrub Model number 449 6 52.11 0.00 0.14 4 52.71 0.59 0.11 Y 5 52.73 0.62 0.11 Y 6 52.76 0.65 0.10 Y 6 52.88 0.77 0.10 Y 7 53.09 0.98 0.09 5 53.10 0.99 0.09 5 53.53 1.42 0.07 7 53.66 1.55 0.07 Y 5 53.76 1.65 0.06 Y 7 53.78 1.67 0.06 Y Y Y Y Y Y Y Y Y 455 Table 2. Weighted averaged parameter estimates (back-transformed where necessary) 456 from the top models ± weighted 90% CI for terms upheld in the top GLMs (Table 1). 457 Terms in bold are those retained in all top models. 458 459 460 Term Estimate Lower CI Upper CI Intercept -10.848 -18.449 -3.246 Area of Established scrub 0.557 0.241 0.954 Area of grazed land -0.165 -0.285 -0.025 Volume of large (>4m) hedgerow 1.558 0.225 4.341 Area of fallow 0.099 -0.006 0.217 Area of standing water 0.065 -0.005 0.140 Woodpigeon abundance -0.278 -0.575 0.019 Area of young scrub -0.036 -0.081 0.012 461 Table 3a. Summary of the top models from a poisson GLM examining which habitat features influence the number of Turtle Dove territories. Y Y 4 Y Y Y 5 Y Y Y 6 Y Y Y 7 Y Y Y Weight Y Delta AICc 3 AICc Y 0.00 0.17 117.45 1.14 0.10 117.50 1.19 0.09 117.58 1.27 0.09 Y 117.71 1.39 0.08 Y 117.97 1.66 0.07 118.04 1.72 0.07 Y Y Y Y Area of trees Y Area of young scrub Y Woodpigeon abundance 2 116.31 Longitude Y Area of spring cereals Area of standing water Y Area of fallow Volume of large hedgerows Y Area of bare ground Area of established scrub 1 Year of previous record Model number 462 Y 463 464 465 466 467 8 Y Y Y 9 Y Y Y 10 Y Y Y 11 Y Y Y 12 Y Y Y Y Y Y Y Y Y Y 118.16 1.84 0.07 118.19 1.88 0.07 118.21 1.90 0.07 118.28 1.96 0.06 118.28 1.97 0.06 468 Table 4. Weighted averaged parameter estimates (back-transformed where necessary) 469 from the top models ± weighted SE for terms upheld in the top GLMs (Table 1). 470 Terms in bold are those retained in all top models. 471 472 473 Term Estimate Lower CI Upper CI Intercept -5.831 -8.588 -3.074 Area of Established scrub 0.236 0.118 0.434 Volume of large (>4m) hedgerow 0.294 0.053 0.710 Area of standing water 0.103 0.026 0.197 Year of previous record -0.065 -0.152 0.022 Area of bare ground 0.010 -0.003 0.023 Area of fallow 0.006 -0.002 0.014 Area of spring cereals -0.008 -0.019 0.004 Longitude 0.015 -0.013 0.044 Woodpigeon abundance -0.007 -0.023 0.009 Area of young scrub -0.002 -0.006 0.002 Area of trees -0.002 -0.005 0.002 474 Figure Legends 475 476 Figure 1. Distribution of a) Turtle Dove abundance in squares with >50% farmland 477 across East Anglia during 2008 and 2009, b) sites re-surveyed during 2010 coded 478 according to the year of original record. Abundance refers to the number of singing 479 males, and numbers in brackets in the legends represent the number of records. Site 480 records were obtained from the BTO Breeding Bird Survey, Bedfordshire Bird Atlas, 481 Cambridgeshire Bird Report, Norfolk County Bird Records, previous RSPB farmland 482 bird surveys, the 2008 Suffolk Wildlife Trust Turtle Dove Survey and personal bird 483 records obtained following e-mails to regional bird forums. 484 485 Figure 2. Results of 2010 Turtle Dove surveys according to presence/absence of 486 territorial Turtle Doves 487 488 Figure 3. Turtle Dove territories were more likely to be retained in areas a) with a 489 greater area of established scrub, and b) with greater volumes of hedgerows greater 490 than 4m in height. A: Turtle Doves absent; P: Turtle Doves present. 491 492 493 Figure 1. 494 495 a) 496 497 498 499 500 501 502 503 504 505 506 507 508 b) 509 510 511 512 513 514 Figure 2 515 a) 516 517 518 519 520 Figure 3 522 a) Established scrub 3 2 1 0 Area of established scrub (ha) 4 521 A 523 524 b) Hedge >4m P A 525 526 527 P 0 10000 20000 30000 40000 Volume of large (>4m high) hedges (cubic m) 50000 528 Appendix 1. Terms screened to determine their influence on Turtle Dove presence, or 529 on the abundance of territorial birds. 530 531 Geographical: 532 Longitude 533 Latitude 534 535 Nesting habitat: 536 Area of established scrub 537 Area of young or newly planted scrub 538 Area of trees with no scrub understorey 539 Volume of large hedge >4m high 540 Volume of medium and small hedges <2-4m high 541 542 Foraging habitat: 543 Area of bare earth 544 Area of spring cereals 545 Area of fallow 546 Area of broad-leaved crops 547 Area of grazed land 548 Area of standing water 549 550 Year of previous record (2008 or 2009)